Steady flow retrograde

In Table 1 the results obtained with 5 prosthetic valves (HK 21, 23, 25, 27, 29 mm TAD) are shown. Water at room temperature was the circulatory fluid. Steady retrograde flow is not an icreasing function of the diameter, meaning that the working tolerances affect very much the clearance between disc and stent. It is possible, by knowing both pressure and flow rate across the valve, to calculate a hydraulic equivalent diameter which shows the size of the disc--stent clearance. The ratio between such a diameter and the nominal one provides a figure of merit for the comparative evaluation of different prostheses. 

Table 1. Dependence of steady retrograde flow from valve diameter.

The functionality of the valve has been tested with equipment which has been made in our laboratory. Pulsatile flow tests on a mock circulatory system, flow patterns, measurements of steady retrograde flow and pressure drop across the valve, in vivo tests have been carried out. By the pulsatile flow tests, the shapes of curves referring to ventricular and aortic pressure and to flow rate, similar to that shown by other kinds of valves, have been observed. 

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